Vegetative Propagule Pressure and Water Depth Affect Biomass and Evenness of Submerged Macrophyte Communities

Vegetative propagule pressure may affect the establishment and structure of aquatic plant communities that are commonly dominated by plants capable of clonal growth. We experimentally constructed aquatic communities consisting of four submerged macrophytes (Hydrilla verticillata, Ceratophyllum demersum, Elodea nuttallii and Myriophyllum spicatum) with three levels of vegetative propagule pressure (4, 8 and 16 shoot fragments for communities in each pot) and two levels of water depth (30 cm and 70 cm). Increasing vegetative propagule pressure and decreasing water level significantly increased the growth of the submerged macrophyte communities, suggesting that propagule pressure and water depth should be considered when utilizing vegetative propagules to re-establish submerged macrophyte communities in degraded aquatic ecosystems. However, increasing vegetative propagule pressure and decreasing water level significantly decreased evenness of the submerged macrophyte communities because they markedly increased the dominance of H. verticillata and E. nuttallii, but had little impact on that of C. demersum and M. spicatum. Thus, effects of vegetative propagule pressure and water depth are species-specific and increasing vegetative propagule pressure under lower water level can facilitate the establishment success of submerged macrophyte communities.     

The influence of <Emphasis Type="Italic">Ceratophyllum demersum</Emphasis> L. and <Emphasis Type="Italic">Stratiotes aloides</Emphasis> L. on richness and diversity of aquatic vegetation in the lakes of mid-eastern Poland

The aim of this study was to estimate the influence of Ceratophyllum demersum L. and Stratiotes aloides L. on the species richness and phytocoenotic diversity of aquatic vegetation in lakes. The study was based on field investigations in the Łęczna-Włodawa Lake District located in mid-eastern Poland. The studied lakes (32) included both polymictic and dimictic reservoirs. Both in the polymictic and dimictic lakes, statistically significant correlation coefficients were obtained between the parameters that characterize Stratiotes aloides (the frequency in the phytosociological relevés, the percent share of Stratiotetum aloidis association in the phytolittoral) and those characteristic for species richness (the total number of hydromacrophytes, the number of charophytes, elodeids, nymphaeids and lemnids), phytocoenotic richness (the mean number of species in the phytosociological relevés) and phytocoenotic diversity (the Shannon–Wiener Index). The communities with a share of S. aloides are characterized by higher species richness. However, not a single case of statistically significant dependency was reported between the parameters that describe C. demersum (the frequency in the phytosociological relevés, the percent share Ceratophylletum demersi association in the phytolittoral) and the vegetation traits in both lake groups. Common occurrence of Stratiotes aloides might be considered to be evidence for good status of an aquatic ecosystem and a very good indicator of species richness and diversity of aquatic vegetation.     

Charophyte occurrence in Ceratophyllum demersum stands

The hornwort Ceratophyllum demersum is a loosely attached to the bottom or free-floating vascular macrophyte, which builds dense stands in nutrient-rich waters. The hornwort stands are usually monospecific communities with a negligible contribution of other aquatic plants. However, some published literature data and our own observations evidenced the co-occurrence of densely growing Ceratophyllum and other macrophytes, including charophytes, which by contrast to hornwort are indicative of clear and less productive waters. Thus, the aim of this study was to identify the charophyte species growing in C. demersum stands and to define the environmental conditions promoting this co-occurrence. In 18 natural lakes of Western Poland, 60 stands of Ceratophyllum demersum were studied in the years 2001–2005. A total of 25 species built the studied stands. As many as eight charophyte species, 13 vascular plants, two moss species and one filamentous alga co-occurred with C. demersum. Among charophytes rare to Poland Chara polyacantha and Nitella gracilis were identified. Nitellopsis obtusa and Chara globularis revealed the highest frequencies along with Myriophyllum spicatum. Morphology of lakes combined with water quality, particularly transparency, appeared to regulate the coexistence of charophytes and C. demersum, macrophytes usually competing with each other.     

Long- and short-term Changes of the Macrophyte Vegetation in Strongly Stratified Hypertrophic Lake Verevi

The aim of study was to bring out changes in the macrophyte vegetation, caused by eutrophication, short-term lowering of the water level and the following restoration of equilibrium in L. Verevi. Also biomass and N and P content of shoots of main submergent species were studied in 1999–2001, to follow the temporal and specific differences. Due to strong eutrophication, the type of the lake changed from a Myriophyllum-Potamogeton-Charophyta lake to a Ceratophyllum-Lemna trisulca lake in 1984–1988, obviously owing to the formation of loose organic-rich sediment. Water lowering by 0.7 m during summer months of 1998 facilitated mineralization of sediments, as a consequence of which a mass development of Ranunculus circinatus and a temporary increase in the abundance and biomass of other nutrient-demanding species took place during following years. Our data suggest differences in nutrient supply and release of submerged species and the need for more species-related approach to this group. The problem of nutrient supply of unrooted plants at the time of stratification arises. Regarding the increase of biomass of Ceratophyllum demersum in second half of summer, we suppose that one part of nutrients for this growth may derive from freshly decayed filamentous algae or vascular plants.     

Estimating biomass of submersed vegetation using a simple rake sampling technique

We evaluated the use of a simple rake sampling technique for predicting the biomass of submersed aquatic vegetation. Vegetation sampled from impounded areas of the Mississippi River using a rake sampling technique, was compared with vegetation harvested from 0.33-m² quadrats. The resulting data were used to model the relationship between rake indices and vegetation biomass (total and for individual species). We constructed linear regression models using log-transformed biomass data for sites sampled in 1999 and 2000. Data collected in 2001 were used to validate the resulting models. The coefficient of determination (R ²) for predicting total biomass was 0.82 and ranged from 0.59 (Potamogeton pectinatus) to 0.89 (Ceratophyllum demersum) for individual species. Application of the model to estimate total submersed aquatic vegetation is illustrated using data collected independent of this study. The accuracy and precision of the models tested indicate that the rake method data may be used to predict total vegetation biomass and biomass of selected species; however, the method should be tested in other regions, in other plant communities, and on other species. Handling editor: S. M. Thomaz     

Zonation of submerged macrophyte vegetation in Lake Kariba,Zimbabwe and its ecological interpretation

The submerged vegetation of Lake Kariba is described in relation to degree of slope (lake morphometry), depth and light transparency. The direct gradient analysis technique — canonical correspondence analysis and the TWINSPAN classification programs were used to analyse the data set. The western end of the lake with low transparency has a low species diversity (with Vallisneria aethiopica dominating). Species diversity increases with increased transparency in the other parts of the lake. The classification revealed monospecific communities for all species as well as mixed communities with Lagarosiphon as the associate species with the broadest distribution. The ordination revealed a first axis strongly related to depth and transparency gradients and the second axis related to slope. Vallisneria aethiopica has a growth form adapted to grow in shallow areas subjected to wave action. Potamogeton octandrus also growing in shallow areas is restricted to sheltered areas. Lagarosiphon ilicifolius precluded from the shallow exposed areas grows at medium depth but has a growth form adapted to tap light at the surface. Najas pectinata and Ceratophyllum demersum are adapted to grow in deep water.Abbreviations CCA Canonical correspondence analysis     

Impacts of sediment type on the performance and composition of submerged macrophyte communities

To restore deteriorated lake ecosystems, it is important to identify environmental factors that influence submerged macrophyte communities. While sediment is a critical environmental factor for submerged macrophytes and many studies have examined effects of sediment type on the growth of individual submerged macrophytes, very few have tested how sediment type affects the growth and species composition of submerged macrophyte communities. We constructed submerged macrophyte communities containing four co-occurring submerged macrophytes (Hydrilla verticillata, Myriophyllum spicatum, Ceratophyllum demersum and Chara fragilis) and subjected them to three sediment treatments, i.e., clay, a mixture of clay and quartz sand at a volume ratio of 1:1 and a mixture at a volume ratio of 1:4. Compared to the clay, the 1:1 mixture treatment greatly increased overall biomass, number of shoot nodes and shoot length of the community, but decreased its diversity. This was because it substantially promoted the growth of H. verticillata within the community, making it the most abundant species in the mixture sediment, but decreased that of M. spicatum and C. demersum. The sediment type had no significant effects on the growth of C. fragilis. As a primary nutrient source for plant growth, sediment type can have differential effects on various submerged macrophyte species and 1:1 mixture treatment could enhance the performance of the communities, increasing the overall biomass, number of shoot nodes and shoot length by 39.03%, 150.13% and 9.94%, respectively, compared to the clay treatment. Thus, measures should be taken to mediate the sediment condition to restore submerged macrophyte communities with different dominant species.     

Effects of Spirogyra arcta on biomass and structure of submerged macrophyte communities

The presence of algae can greatly reduce the amount of light that reaches submerged macrophytes, but few experimental studies have been conducted to examine the effects of algae on biomass and structure of submerged macrophyte communities. We constructed communities with four submerged macrophytes (Hydrilla verticillata, Egeria densa, Ceratophyllum demersum, and Chara vulgaris) in three environments in which 0 (control), 50 and 100% of the water surface was covered by Spirogyra arcta. Compared to the control treatment, the 100% spirogyra treatment decreased biomass of the submerged macrophyte communities and of all the four macrophytes except C. demersum. Compared to the control and 50% treatments, the 100% treatment significantly increased relative abundance of C. demersum and decreased that of E. densa. Therefore, the presence of S. arcta can greatly affect the productivity and alter the structure of submerged macrophyte communities. To restore submerged macrophyte communities in conditions with abundant algae, assembling communities consisting of C. demersum or similar species may be a good practice.     

The effect of lake morphology on aquatic vegetation development and changes under the influence of eutrophication

Data on aquatic and emergent vegetation, morphology and water quality from 274 Polish lowland lakes surveyed in the years 1996–2009 were used to validate the preliminary typology of Polish lakes based on macrophytes and to indicate the environmental parameters which most significantly determine the vegetation patterns in lakes under various morphological conditions. In highly alkaline lowland lakes representing non-disturbed conditions the key determinants influencing the vegetation patterns were mean depth and the shape of the littoral. Three morphological lake types were distinguished: shallow (<3.5 m), deep, and additionally, within the latter, deep ribbon-shaped, with a clearly elongated base and steep bed slopes. The lake types varied in their vegetation patterns developed under non-disturbed conditions. In the shallow lakes, the share of the phytolittoral in the total lake area (%phytol) was the highest (40–100%, 72.3% on average) and the maximum colonisation depth (C_max) the lowest (3.2 m as the maximum) compared to the lakes from both deep types. In the ribbon-shaped deep lakes, %phytol and the plant coverage (%cover) were the lowest, the proportion of submerged vegetation was extraordinarily high (over 90%) and the emergent vegetation was extremely sparsely developed (<6%) compared to the lakes of the two other types.The alterations of aquatic vegetation resulting from the eutrophication process in distinguished morphological lake types were explored. Within the macrophyte variables tested, three groups of indicators were distinguished: (a) metrics performing best in selected lake types, i.e. the type-specific indicators (abundance metrics, %Pota), (b) metrics performing equally well in all the lake types, considered as the universal indicators (e.g. S_Chara, %Subm and %Emerg) and (c) metrics performing poorly in all the lake types, with generally limited applicability (most of the metrics on syntaxonomic richness). In the shallow lakes, %cover and %phytol performed notably better than in deep lakes, whereas C_max worked best in deep lakes and showed the strongest response in the deep regular-shaped lakes. Moreover, in deep regular-shaped lakes the number of communities of stoneworts and submerged plants (S_Chara and S_Subm), and in deep ribbon-shaped lakes the proportion of area inhabited by vascular plant communities (%Pota) performed exceptionally better than in the other two lake types. The most universal metrics, performing equally well in all the lake types, were the proportions of submerged (%Subm) and emergent (%Emerg) vegetation in the total phytolittoral area.     

Toxicity of gold nanoparticles for plants in experimental aquatic system

Increased production and use of nanomaterials can lead to new types of pollution of the environment, including aquatic ecosystems. Pollution of the aqueous environment with nanoparticles can be a new type of pollution of the environment. This requires a more detailed study of the biological effects during exposure of nanoparticles on aquatic organisms. The interactions of gold nanoparticles (Au) with aquatic macrophytes Ceratophyllum demersum have been studied. Aquatic microcosms with these plants were used. Gold nanoparticles (Au) were added to the aqueous medium of C. demersum macrophyte containing microcosms. The state of the plants was then analyzed. Phytotoxicity of Au nanoparticles for aquatic macrophytes was shown for the first time. A new method of phytotoxicity detection was suggested and successfully approved. Phytotoxicity at a concentration of Au (in the form of nanoparticles) of 6 × 10^?6 M-1.8 × 10^?5 M was shown.     

Waterfowl grazing effects on submerged macrophytes in a shallow mediterranean lake

Waterfowl exclusion cages were set up in Sentiz Lake, an eutrophic shallow lake in León (NW of Spain) in order to determine the role of waterfowl herbivory on macrophyte biomass and species composition. Total macrophyte biomass was high during the study (250 g DW m⁻² in summer). The macrophyte community was mainly formed by Myriophyllum alterniflorum (95% cover), Ceratophyllum demersum (5%) and Potamogeton gramineus (<0.5%). High densities of co-occurring coots (Fulica atra; 24 ind/ha) and ducks (Anas penelope, A. strepera and A. platyrhynchos; 18 ind/ha) did not have a significant effect on macrophyte biomass in the lake. There were no statistical differences between total biomass inside and outside the exclosures, although plant biomass reached a higher value inside the cages than in the lake. Biomass species composition was significantly different inside and outside exclosures; C. demersum was more abundant in the cages than in the lake. P. gramineus, almost absent in the lake, became co-dominant with M. alterniflorum in some exclosures. The detailed study of M. alterniflorum flower buds in summer showed significant herbivory by coots. Flower bud abundance was lower in the lake (35% lower in June; 85% lower in July) than under waterfowl exclusion. The effect of waterfowl on macrophyte biomass in Mediterranean wetlands seems to be negligible as compared to effects identified in northern European lakes. Apart from an important role in dispersal, waterfowl in Mediterranean areas have a strong qualitative effect on the structure of plant communities by selecting most palatable species or their reproductive structures.     

Native and Non-Native Plants Provide Similar Refuge to Invertebrate Prey,but Less than Artificial Plants

Non-native species introductions are widespread and can affect ecosystem functioning by altering the structure of food webs. Invading plants often modify habitat structure, which may affect the suitability of vegetation as refuge and could thus impact predator-prey dynamics. Yet little is known about how the replacement of native by non-native vegetation affects predator-prey dynamics. We hypothesize that plant refuge provisioning depends on (1) the plant’s native status, (2) plant structural complexity and morphology, (3) predator identity, and (4) prey identity, as well as that (5) structurally similar living and artificial plants provide similar refuge. We used aquatic communities as a model system and compared the refuge provided by plants to macroinvertebrates (Daphnia pulex, Gammarus pulex and damselfly larvae) in three short-term laboratory predation experiments. Plant refuge provisioning differed between plant species, but was generally similar for native (Myriophyllum spicatum, Ceratophyllum demersum, Potamogeton perfoliatus) and non-native plants (Vallisneria spiralis, Myriophyllum heterophyllum, Cabomba caroliniana). However, plant refuge provisioning to macroinvertebrate prey depended primarily on predator (mirror carp: Cyprinus carpio carpio and dragonfly larvae: Anax imperator) and prey identity, while the effects of plant structural complexity were only minor. Contrary to living plants, artificial plant analogues did improve prey survival, particularly with increasing structural complexity and shoot density. As such, plant rigidity, which was high for artificial plants and one of the living plant species evaluated in this study (Ceratophyllum demersum), may interact with structural complexity to play a key role in refuge provisioning to specific prey (Gammarus pulex). Our results demonstrate that replacement of native by structurally similar non-native vegetation is unlikely to greatly affect predator-prey dynamics. We propose that modification of predator-prey interactions through plant invasions only occurs when invading plants radically differ in growth form, density and rigidity compared to native plants.     

Consortia in Aquatic Ecosystems of the Transbaikalia

A survey in the basin of the Khilok River (a right tributary of the Selenga River) in 1999–2002 allowed us to reveal and describe the consortia of cyanobacteria Stratonostoc linckia f. linckia and Stratonostoc verrucosum, green alga Cladophora aegagropila, stonewort Nitella opaca, water moss Fontinalis sp., and duckweed Lemna trisulca. The relationship between the consort organisms and edificator plants can become the limiting factor in these communities. The long-term studies of the benthic communities of the Arakhlei Lake demonstrate the significance of the consortium approach in the long-term prediction of changes in the lake ecosystem.     

The Relationships Between Environmental Factors and the Submerged Potametea Associations in Lakes of North-eastern Poland

A comparative analysis of submerged Potametea communities in lakes of north-eastern Poland was conducted with respect to 16 water chemistry and 14 substrate parameters. The analysis of 187 relevés based on TWINSPAN clustering showed the existence of 8 aquatic vegetation types. Each of them is characterized by a strong dominance of one of the following macrophytes: Potamogeton lucens, P. perfoliatus, Myriophyllum spicatum, M. verticillatum, Elodea canadensis, Ceratophyllum demersum, Ranunculus circinatus and Hydrilla verticillata. The above vegetation types correspond to the plant associations distinguished using the Braun-Blanquet method (Potametum lucentis, Potametum perfoliati, Myriophylletum spicati etc.) It was demonstrated that among properties of water analysed, COD-KMnO₄, SO₄²⁻, pH, Na⁺, K⁺, Ca²⁺, total hardness, total Fe, Cl⁻ and colour appear to be most important in differentiating the habitats of the communities studied. In the case of substrates the properties which best differentiated the habitats compared were hydration, organic matter content, total N, PO₄³⁻, K⁺, dissolved SiO₂, SO₄²⁻, Cl⁻ and pH. Most of the aquatic plant communities investigated are distinct with respect to their phytocoenotic structure and ecology and could be good indicators of various types of habitats in lake ecosystems.     

Assessing the responses of aquatic macrophytes to the application of a lanthanum modified bentonite clay,at Loch Flemington,Scotland, UK

Loch Flemington is a shallow lake of international conservation and scientific importance. In recent decades, its status has declined as a result of eutrophication and the establishment of non-native invasive aquatic macrophytes. As previous research had identified the lake bed sediments as an important source of phosphorus (P), the P-capping material Phoslock^® was applied to improve water quality. This article documents the responses of the aquatic macrophyte community by comparing data collected between 1988 and 2011. Summer water-column total P concentrations decreased significantly and water clarity increased following treatment. Aquatic plant colonisation depth increased and plant coverage of the lake bed extended. However, the submerged vegetation remained dominated by the non-native Elodea canadensis Michx. Aquatic macrophyte community metrics indicated no significant change in trophic status. Species richness and the number of ‘natural’ eutrophic characteristic species remained broadly similar with no records of rare species of conservation interest. Loch Flemington is still classified as being in ‘unfavourable no change’ condition based on its aquatic macrophytes despite the water quality improvements. The implications of these results are discussed in relation to the future management of Loch Flemington and in the wider context of trying to improve our understanding of lake restoration processes.     

Patchy distributions of Spirogyra arcta do not affect growth of the submerged macrophyte Ceratophyllum demersum

Spatial heterogeneity is common in aquatic conditions, but few studies have examined the effects of heterogeneous distributions of biological factors on aquatic plants. Spirogyra (Spirogyra arcta) coexists with many submerged macrophytes, such as Ceratophyllum demersum, but no study has examined the effects of heterogeneous distributions of spirogyra on the growth of submerged plants. We grew the submerged plant C. demersum in three homogeneous, aquatic conditions (0, 50 and 100% of the water surface in the container was evenly covered by spirogyra, referred to as ‘control’, ‘50%’ and ‘100%’, respectively) and two patchy conditions (the left half of the water surface in the container was not covered by spirogyra and 50% and 100% of the water surface in the right half of the container was evenly covered by spirogyra, referred to as ‘50%‐patchy’ and ‘100%‐patchy’, respectively). Compared with the control, the 100% treatment greatly decreased the biomass and number of ramets of C. demersum, but the 50% treatment did not. Growth of C. demersum in the left half of the container did not differ significantly between the control and the two heterogeneous treatments (50%‐patchy and 100%‐patchy). In addition, growth of C. demersum in the right half of the container did not differ between the 100% and the 100%‐patchy treatment or between the 50% and the 50%‐patchy treatment. Our results suggest that C. demersum can tolerate shading by spirogyra to a certain extent and that heterogeneous distributions of spirogyra do not affect its growth.     

Patterns of microbial food webs in Mediterranean shallow lakes with contrasting nutrient levels and predation pressures

Hygraula nitens is a New Zealand native moth with aquatic larvae that feed on submerged aquatic plants. The larvae have been mainly observed using native Potamogeton and Myriophyllum species as a food source, although some studies reported larvae feeding on the alien macrophytes Hydrilla verticillata, Lagarosiphon major and Ceratophyllum demersum. Experimental mesocosm studies showed larvae had a major effect on H. verticillata, C. demersum, L. major, Elodea canadensis and Egeria densa. In both no choice and choice experiments H. nitens larvae showed a clear preference for and the highest consumption of C. demersum, while the native macrophyte Myriophyllum triphyllum ranked fourth out of five alien and two native plant species, indicating a preference of the larvae for alien macrophytes. Additional choice experiments using C. demersum, sampled from different waters in NZ, illustrated that there was a clear difference in H. nitens preference for plants based on their source. However although C. demersum had the lowest leaf dry matter content (LDMC) compared with the other macrophytes, neither the LDMC nor leaf carbon, nitrogen, phosphorus or total phenolic contents alone could explain the preferences of H. nitens, and we conclude that food choice is based on a combination of these and/or additional factors.     

Genetic diversity of Potamogeton pectinatus L. in relation to species diversity in a pair of lakes of contrasting trophic levels

Understanding the correlation between genetic diversity and species diversity in freshwater communities is important to elucidate the influences of local selective forces on the genetic diversity of local aquatic plant populations across different communities. This study employed amplified fragment length polymorphism (AFLP) to assess the genetic diversity of Potamogeton pectinatus L. populations between two sister-lakes with contrasting trophic levels, eutrophic and oligotrophic, in the Yunnan Plateau in southwest of China. The results showed high genetic differentiation between eutrophic lake and oligotrophic lake. The genetic distances between P. pectinatus populations were significantly correlated with the species evenness, but not with difference in species richness of aquatic plant communities. The results underpinned that genetic diversity at inter-population levels and local species diversity in plant communities are positively correlated. In addition, our results also suggested that habitat types might play an important role in the genetic diversity of the P. pectinatus populations between these two lakes.     

鄱阳湖南矶湿地优势植物群落及土壤有机质和营养元素分布特征

湿地植物和土壤是承担湿地诸多生态功能的主要基质和载体,相互之间有着强烈的影响。湿地土壤影响植物的种类、数量、生长发育、形态和分布,湿地植物又影响土壤中元素的分布与变化。鄱阳湖湿地的植物和土壤的特征及由他们带来的候鸟栖息地价值都受到他们之间的相互作用以及湖泊水位不同频率和幅度波动的影响。研究鄱阳湖湿地植物和土壤的特征及其形成原因和相互关系。为此,从2010年10月到2011年10月,对鄱阳湖湿地不同水位梯度下分布的芦苇、南荻、苔草、虉草和刚毛荸荠5个优势植物群落中57个定点样方展开了月度植被调查并且对5个不同植物群落下的135个土壤样品进行了实验室分析,研究了鄱阳湖优势植物群落及湿地土壤中有机质、全氮、全磷、全钾含量的分布特征及其相互关系。研究结果表明,鄱阳湖湿地优势植物群落分布特征受湿地土壤元素分布特征、湖面水位波动及植物生长特性和土壤沉积及土壤养分的综合影响,呈现了沿水位和海拔梯度明显的条带状或弧状分布、从湖岸到湖心依次分布为:狗牙根群落、芦苇群落、南荻群落、苔草群落、虉草群落、刚毛荸荠群落,最后是水生植物。同时植物群落的组成和分布特征也随季节性水位涨落的变化而变化;土壤有机质及其他各元素含量特征受植物群落分布、水位波动规律及湿地土壤特性等各种因素的影响,呈现出相对一致的分布规律,在0—20cm土壤层含量较高,20cm层后随土壤深度的增加含量逐渐减小,减小的速度先快后慢直至40cm层后趋于稳定;不同植物群落对土壤有机质、全氮、全磷、全钾的含量及变化具有很大的影响,不同植物群落下同种元素含量差异显著,并且各自随土壤深度和植物群落的变化呈现出层状、带状或弧状富集特征。不同植物群落对土壤养分元素含量影响程度不同,苔草群落对各元素吸收和滞留能力最强、影响最大,刚毛荸荠群落对土壤营养元素影响最弱。湿地植物群落和土壤之间彼此有着强烈的影响,其中植株的重量和土壤的SOC、TN及TP含量有非常显著的负相关关系,与土壤TK含量则有较强的正相关关系,同时,植株的重量和高度与土壤地下水埋深也有微弱的负相关关系。     

Aquatic oligochaete fauna (Annelida,Clitellata) in Lake Tonle Sap and adjacent waters in Cambodia

In surveys conducted during 2000–2005, 39 taxa of aquatic oligochaetes belonging to the families Enchytraeidae and Naididae were found in Lake Tonle Sap in the Mekong River Basin, Cambodia. Dominated by naidines and pristinines (29 taxa), they mainly comprised widely distributed species as well as South Asian and Southeast Asian species. Among the four areas studied, the littoral regions of the lake—where inundated forests and aquatic vegetation developed during the flooded seasons—presented the highest number of species. Submerged vegetation in the littoral Lake Tonle Sap harbored abundant epiphytic oligochaetes, especially Stylaria fossularis. In contrast to the rich abundance of naidine and pristinine fauna, tubificines and ryhacodrilines were scarce in and around the lake, irrespective of the vegetation in their habitats. Several Aulodrilus species and Branchiura sowerbyi were the main representatives of the benthic oligochaete assemblages throughout the offshore zone of the lake without vegetation. It is noteworthy that the widely distributed tubificines Tubifex tubifex and Limnodrilus hoffmeisteri were not found in any surveyed locality.